Command Syntax Part 2
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How do you tell which Parameters are optional and which arguments are required?
To answer that question we need PowerShell’s Help system
Type help get-service -showwindow
Scroll down to the Syntax section and what I have done is I’ve copied the Syntax section into
my scripting Pane. So you can use show window and I’ll view the syntax from the scripting
pane.
Now watch this I’m going to type get-service, notice that this cmdlet runs without adding
any parameters.
Now check this out type get-eventlog press return, notice what it says:
So, the question is why did get-service run when get-eventlog required a value for the -logname parameter?
1 The answer is in the syntax of the help files for get-service and get-eventlog
Lets checkout get-service first. Let’s start with parameter set #2 and set #3
Optional [Parameter Argument] Notice that all the parameters and the arguments are
surrounded by square brackets.
This means that adding the parameters are optional and not needed. So,
2 Get-service will run without adding any parameters.
Now let’s take a look at the syntax for get-eventlog
If you want to follow along type help get-eventlog -showwindow
Again I’ve copied the syntax for get-eventlog to my scripting pane
Let’s go through the syntax, notice that almost every parameter and every argument are
surrounded by square brackets, that means that they are all optional or not needed.
Notice -logname is surrounded by square brackets but the argument is not.
Required Argument
That means, because there are square brackets around the parameter -logname, the name
logname is optional but the argument <string> is required.
That is why when you ran get-eventlog without any parameters, PowerShell asks for a
value for -logname
Now go back to get-eventlog, logname:
type Application and press return, and the command runs.
3 Let’s go ahead and clear the screen cls
4 Positional parameters [Param] (Use get-eventlog scroll down to #Position)
Type help get-eventlog -showwindow
Scroll down until you see the parameter attributes list. We are going to be working with
three parameters from this list, -InstanceID, -logname and -newest
From the list notice that the parameter -logname has a position of 0,
-InstanceID has a position of 1 and -newest has a position of named.
Now what does this mean?
0, 1 and name, refer to the actual position that the cmdlet must be placed in the order of
the cmdlets.
So -logname is positional, it’s position is 0 which is the first position.
The parameter -instanceID position is 1 which is after -logname in the order of cmdlets
Ok let's check that out
So type get-eventlog application 0,1
(I don’t have to type the parameter -logname or the parameter -InstanceID, because they
are both optional because they're surrounded by square brackets
Now take a look at the argument for -InstanceID because there are two square brackets
within the angle brackets the parameter -InstanceID can take multiple arguments. Now
press return and that runs.
Now let's see if we can move these values out of order. Move the 0,1 in front of
application and press return.
And we get an error because Powershell expects the positional parameter -logname or the
value type application to be 5 the first in the list.
6 Named Parameters
Take a look at -Newest, notice that the position is named.
Named means that you can put -newest anywhere in the order of parameters and it will
work. Let’s check it out
Type get-eventlog -newest 5 application 0,1 and that worked.
We see that we moved the parameter with a position called named and moved that in front
of the positional parameter -logname and we see that the command ran
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get- service has a required parameter of -DisplayName. But runs without it. It seems to me that the only true required parameters are the ones that are not “named” in the positional setting and the “named” ones are ones that can be left off.
example get-help get-help -showwindow it shows that -full, -showwindow and few others are required but are also “named” in postional.
is this correct or did i make a mistake
Hi
Ambrose Garza
The get-service runs on its own since it gets all the services on the computer if not using -DisplayName.
I do see what you mean. When executing get-help get-service -showwindow just -DisplayName is required.
I can’t seem t find why some are required and why others don’t.
It seems that if you use a parameter you need to specify a value.
Ricardo